/Engine/Source/Runtime/Engine/Public/Subsystems/SubsystemCollection.h
Unregisters and removed instances of the specified Subsystem class from all existing SubsystemCollections of the correct type. Should be used by specific subsystems in plug ins when plugin is deactivated.
static void DeactivateExternalSubsystem ( [UClass](API\Runtime\CoreUObject\UObject\UClass) * SubsystemClass )